In this study, corn stover with different ash content was pretreated using dry dilute acid pretreatment method at high solids loading of 67% (w/w). The results indicate that the hydrolysis yield of corn stover is increased from 43.30% to 70.99%, and ethanol yield is increased from 51.74% to 73.52% when ash is removed from 9.60% to 4.98%. The pH measurement of corn stover slurry indicates that the decrease of pretreatment efficiency is due to the neutralization of sulfuric acid by alkaline compounds in the ash. The elemental analysis reveals that the ash has the similar composition with the farmland soil. This study demonstrates the importance of ash removal from lignocellulose feedstock under high solids content pretreatment. (C) 2014 Elsevier Ltd. All rights reserved.